The present disclosure relates to a metallic shield for reducing electromagnetic interference (EMI), and more specifically, to a metallic grid that additionally reduces diffractive effects at optical wavelengths.
Electromagnetic interference (EMI) is a disturbance to an electrical circuit due to electromagnetic radiation emitted from an external source. Protecting a circuit from EMI generally involves placing a metallic grid between the circuit and the external source. The metallic grid generally consists of a patterned metal coating applied to an optical substrate. In addition to protecting against EMI, the patterned metal coating is designed to allow transmission of optical wavelengths through the coating. In various implementations of a patterned EMI-reducing coating, the presence of the coating unavoidably reduces optical transmission, both by blocking light and by diffracting a portion of the transmitted light, resulting in signal loss and increased background illumination. In various applications, it may be useful to pass light (i.e., a designator beam) from a light source such as a laser through the metallic grid to identify an object. However, if the pattern of the grid is periodic, light passing through the grid may generate a diffractive scatter halo having side lobes, which are bright peaks of light appearing in the diffractive halo surrounding the desired (specular) beam. Additionally, the side lobes may fall on objects other than a target that is to be identified, giving rise to the possibility of a false positive identification. Therefore, there is a need to reduce the diffractive effects at optical wavelengths.